Gamma-ray astronomy

Gamma-ray astronomy studies celestial objects and phenomena by detecting gamma rays, the highest-energy form of electromagnetic radiation. It reveals energetic processes that are difficult or impossible to observe at lower photon energies.

Cherenkov telescope: A telescope that detects brief flashes of Cherenkov light produced when high-energy particles travel through a medium faster than light travels in it. Ground-based instruments infer very-high-energy gamma rays from particle showers that create Cherenkov light in the atmosphere.
Gamma-ray burst: A brief, extremely luminous flash of gamma rays, usually associated with a distant cosmic explosion. Bursts are among the brightest transient targets and probe extreme explosions across cosmic distances.
Victor Hess: An Austrian physicist whose balloon flights established that ionizing radiation increases with altitude, revealing cosmic rays. His discovery of cosmic rays helped establish the broader high-energy astronomy whose gamma-ray branch followed.
X-ray astronomy: The study of astronomical sources through X-rays, electromagnetic radiation less energetic than gamma rays. The boundary between X-rays and gamma rays is convention-dependent, but their detectors and typical source regimes differ.
Cosmic-ray origin: The problem of identifying the astrophysical sources that accelerate cosmic rays to high energies. Gamma-ray emission can trace interactions of energetic cosmic rays, but identifying their accelerators remains difficult.
Air shower: A cascade of secondary particles produced when a high-energy cosmic ray or gamma ray strikes the atmosphere. Gamma rays above the atmosphere generate particle cascades whose Cherenkov light ground-based observatories record.
Pulsar: A rapidly rotating neutron star that emits beams of radiation observed as regular pulses. Gamma-ray observations reveal energetic pulsars and help locate where their magnetospheres accelerate particles.
Explorer 11: A NASA satellite launched in 1961 that conducted the first gamma-ray observations from space. Its pioneering measurements marked the beginning of space-based gamma-ray astronomy.
Cosmic-ray astronomy: The study of high-energy charged particles arriving from space and the sources that produce them. Cosmic rays are charged particles rather than photons, so magnetic fields deflect them unlike gamma rays.
PeVatron: An astrophysical accelerator capable of producing particles with energies near or above one petaelectronvolt. Gamma rays from candidate PeVatrons help test whether they accelerate cosmic rays to the highest observed energies.

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